Apparatus for vaporisation of metals and metalloids



Sept. 1, 1959 D. w. BARKER APPARATUS FOR VAPORISATION OF METALS AND METALLOIDS Filed Feb. 12. 1957 United States Paten ()fii Patented .Sept. .1, 1959 ai fiAR-ATUs FOR .vAPoRIsATioN or METALs AND NIETALLOIDS Dennis Walter Barker, N oithgate, 'Crawley, England, as-

signofto Edwards High Vacuum Limited, Crawley,

England, a British company Application February 12',--=19s7; Serial-No. 639,-655

': o1.'-.-1s as invention relates to vaporisation apparatus particularly of the 'kind in which materials, for example -=metals or metalloids, are vaporised on a continuousv basis for the purpose of, for example, depositing thin films upon objects such as plastic films or sheets of material. The films or sheets of material to be coated are usually carried on a stock reel or drum from which they are driven on to a take up reel or drum. The invention is however also applicable to the deposition of thin or thick films on both stationary and moving articles.

Such vaporisation is usually carried out in a vacuum chamber containing objects to which, for example, metal films or coatings are to be applied and the vacuum chamber contains a small container or crucible in which the metal to be vaporised is placed and heated to the vaporisation temperature by a resistance element or by electromagnetic induction heating.

Owing to the fact that certain metals, particularly aluminum, react with known refractory materials which have been used in the position of crucible heretofore, unsuccessful attempts have been made to utilize other materials. A form of evaporator having substantial advantages over previously known forms is described in the specification of United States Patent No. 2,772,318 and which takes the form of a short cylindrical block or plug of refractory material mounted in a recess in a carbon resistance heater. The surface of the plug is spaced from the wall of the recess so that molten metal cannot easily flow from the working face of the plug and come into contact with the carbon heater surface with consequent undesirable reaction between the metal and the carbon. In order to reduce as far as possible the area of contacting surfaces between the plug and the heater, the plug is provided with short supporting legs. If the plug is of suflicient length to ensure that most of the metal rendered molten at its surface evaporates from its top or sides before reaching its base, specially formed legs need not be provided. The specification referred to also points out that the interior surface of the recess within which the block or plug is placed constitutes a radiant heater and a reflector for vapour falling on to its surface.

The object of the present invention is to provide an evaporator having a longer useful life than those hitherto proposed.

According to the present invention, an evaporator in or for vaporisation apparatus of the kind referred to comprises a block of refractory material having six flat sides and preferably of cube or substantially cube shape. The evaporator may consist of a block of refractory carbide e.g. tantalum carbide, tungsten carbide or it may be of plain tungsten.

Further according to the invention, apparatus for vacuum vaporisation of metals or metalloids comprises a carbon heater for an evaporator which consists of refractory material having six flat sides and in which the carbon heater is held by clamping means which also serve as heating current conveying electrodes, the clamp ing means being arranged to permit the carbon heater to expand and bow inan upward or downward direction.

Furthef according to the invention, in or for apparatus for the vacuum vaporisation of metals or metalloidsmeans for feeding to an evaporator a wire or strip of'the-metal or metalloid to be vaporised comprises a member arranged to guide the wire or strip towards interengaging wheels or rollers at least one of which is positively driven and further means for guiding the wire or strip into contact with a selected region of an evaporator.

One form of apparatus including an evaporator embody'ing the invention willnow be described in greater detail by way of example with reference to the accom= panying drawings in whichi Figure 1 is a diagrammatic partly sectional elevation of the apparatus; and

Figure 2is a plan view ofFigure 1.

Referring to the drawings, the carbon heater bar 1 is generally of the form described in the specification of the patent previously referred to but it is supported by clamps 2, 3. Screws 4, 5 serve to adjust the degree of positive clamping obtained. The clamps rest on a base 6 and they serve as electrodes supplying heating current for the carbon bar.

When the carbon is raised in temperature there is a tendency for it to expand and bow in one direction only, that is to say, in an upward or downward direction. The method of mounting shown enables the carbon bar to expand and bow Without breaking while good contact is maintained by the clamps. In order to prevent the electrodes from becoming overheated, water cooled pipes 7 and 8 are provided. These pipes may, in some circumstances, serve also to urge the clamp electrodes 2, 3 towards each other.

The recess 9 accommodates an evaporator in the form of a cube 10 of refractory material, a refractory carbide for example tantalum carbide or other refractory such as a tungsten refractory. It will be seen from the drawing that the recess 9 is large enough to leave an all-round space between the cube 10 and the walls of the recess. This space is provided to prevent molten metal flowing from the plug into direct contact with the carbon heater 1. The walls of the recess also provide a radiant heating surface from which any metal vapour entering the recess will be reflected and deterioration of the heater will thus be reduced or eliminated. The use of a cube provides six working faces and when one face has deteriorated it is only necessary to rotate the cube to bring a new face uppermost. Normally in the case of a cube of tantalum carbide one face provides about two hours working life so that a total of twelve hours working life is obtained with a cube of refractory compared with four hours working life by a cylindrical refractory which provides only two working faces. In the case of the particular example being described the cube has an edge length of 14 mm. and the working life was obtained with aluminum being fed on to its surfaces at the rate of 2.01 grams per minute.

The metal to be vaporised, say aluminum, is fed in the form of a wire 11 on to the surface of the evaporator 10 from a stock reel 12 the evaporator being heated mainly by radiation from the carbon bar 1. The wire passes through a guide tube 13 to knurled wheels or rollers 14 each of which is positively driven. For this purpose the wheels 14 are mounted on the faces of gear wheels, not shown, one of which meshes with the other and is coupled to a driving motor. From the driving wheels 14, the wire passes through a further guide tube 15 supported in a bracket 16, the tube 15 directing the wire in a positive manner on to the surface of the cube 10. An important advantage of the wire feed arrangement described is that it facilitates accurate location of the region of the refractory plug which receives the aluminum. It is found that pointing of the wire directly at the plug results in the formation of a groove in the plug surface, the groove lying in the direction of incidence of the wire as shown at 17. Fresh areas of the plug surface may be selected by turning the plug about its vertical axis, so that, before it is necessary to commence working on a fresh face of the plug a series of grooves will be formed in the first working face, the grooves intersecting each other at the centre of the working face. The accurate wire feeding arrangement thus enables each face of the cube plug to be worked uniformly.

I claim:

1. Apparatus for vacuum vaporisation of metals and metalloids comprising an elongated carbon heater for an evaporator which consists of a block of refractory material having six flat sides and in which the carbon heater is formed with a recess within which said evaporator is accommodated in such a Way that the walls of the recess are spaced from the evaporator, said carbon heater being held by clamping means which also serve as heating current conveying electrodes, said clamping means being arranged to permit the carbon heater to expand and bow in an upward or downward direction.

2. Apparatus for vacuum vaporisation of metals and metalloids comprising an elongated carbon heater for an evaporator which consists of a block of tantalum carbide having six flat sides and in which the carbon heater is formed with a recess within which said evaporator is accommodated in such a way that the walls of the recess are spaced from the evaporator, said carbon heater being held by clamping means which also serve as heating current conveying electrodes, said clamping means being arranged to permit the carbon heater to expand and bow in an upward or downward direction.

References Cited in the file of this patent UNITED STATES PATENTS 2,337,679 Osterberg Dec. 14, 1943 2,510,205 Baird June 6, 1950 2,693,521 Alexander Nov. 2, 1954 2,772,318 Holland Nov. 27, 1956 

1. APPARATUS FOR VACUUM VAPORISATION OF METALS AND METALLOIDS COMPRISING AN ELONGATED CARBON HEATER FOR AN EVAPORATOR WHICH CONSISTS OF BLOCK OF REFRACTORY MATERIAL HAVING SIX FLAT SIDES AND IN WHICH THE CARBON HEATER IS FORMED WITH A RECESS WITHIN WHICH SAID EVAPORATOR IS ACCOMMODATED IN SUCH A WAY THAT THE WALLS OF THE RECESS ARE SPACED FROM THE EVAPORATOR, SAID CARBON HEATER BEING HELD BY CLAMPING MEANS WHICH ALSO SERVE AS HEATING CURRENT CONVEYING ELECTRODES, SAID CLAMPING MEANS BEING ARRANGED TO PERMIT THE CARBON HEATER TO EXPAND AND BOW IN AN UPWARD OR DOWNWARD DIRECTION. 